An ideal gas obeying the kinetic theory of gases can be liquefied if

• A
  Its temperature is more than critical temperature $T_c$
• B
  Its pressure is more than critical pressure $P_c$
• C
  Its pressure is more than $P_c$ at a temperature less than $T_c$
• D
  It cannot be liquefied at any value of $P$ and $T$